There has been devised a device for detecting contact between hands and a steering wheel as described in PTL 1 for example. A block circuit diagram of the detecting device is shown in FIG. 25.
In FIG. 25, first oscillator 103 including first capacitor 101 generates a first signal with frequency f1. First capacitor 101 is provided in a steering wheel (unillustrated) of a vehicle (unillustrated). First capacitor 101 may be part of an existing heater, for example, of the steering wheel. Such a heater typically adjusts temperature and prevents overheating using a thermostat.
Second oscillator 109 including second capacitor 105 and adjustable third capacitor 107 generates a second signal with second frequency f2. When the hands of a driver are not present on the steering wheel, first frequency f1 and second frequency f2 are equal to each other. Mixer 111 forms an absolute value of the difference between the two frequencies. The absolute value is converted to output voltage U by frequency-voltage converter 113.
If a driver's hands approach the steering wheel and finally grip it, this influences first capacitor 101 to change first frequency f1. Then, as the hands approach the steering wheel, voltage U continuously rises. When voltage U exceeds first threshold S1, contact between the hands and the steering wheel is immediately detected.